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ALLOWANCE FOR CREDIT LOSSES FOR LOANS AND FINANCE LEASES - Carrying Amount of Portfolios (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	$ 12,675,398	$ 12,746,556
Allowance for credit losses	247,269	243,942	$ 263,592	$ 261,843
Residential Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	2,837,846	2,828,431
Allowance for credit losses	$ 41,640	$ 40,654	56,689	57,397
Residential Mortgage Loans [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	1.47%	1.44%
Commercial Portfolio Segment [Member] \| Construction Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	$ 234,441	$ 228,396
Allowance for credit losses	$ 3,417	$ 3,824	6,186	5,605
Commercial Portfolio Segment [Member] \| Construction Loans [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	1.46%	1.67%
Commercial Portfolio Segment [Member] \| Commercial Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	$ 2,501,689	$ 2,565,984
Allowance for credit losses	$ 24,143	$ 22,447	32,661	32,631
Commercial Portfolio Segment [Member] \| Commercial Mortgage Loans [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	0.97%	0.87%
Commercial Portfolio Segment [Member] \| Commercial and Industrial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	$ 3,359,868	$ 3,366,038
Allowance for credit losses	$ 36,464	$ 33,034	35,423	33,996
Commercial Portfolio Segment [Member] \| Commercial and Industrial Loans [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	1.09%	0.98%
Consumer Portfolio Segment [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	$ 3,741,554	$ 3,757,707
Allowance for credit losses	$ 141,605	$ 143,983	$ 132,633	$ 132,214
Consumer Portfolio Segment [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	3.78%	3.83%
Loan Total [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	1.95%	1.91%